Conventionally, sheet feeders have had a separating function for separating and feeding a plurality of sheets from a paper tray in order to feed the sheets one at a time. With this type of sheet feeder, if a user inadvertently inserts a stack of sheets too far into the device when placing sheets on the paper tray, the sheets are likely to be more difficult to be separated and fed one at a time, often resulting in two or more sheets being fed simultaneously, i.e., a double-feed. Consequently, conventional sheet feeders are normally equipped with regulating means for preventing the stack of sheets from being inserted into the device too far in order to maximize the sheet-separating capacity of the sheet feeder.
For example, there is known a sheet-feeding device that includes a separation roller, a feed roller, and regulating means. The regulating means is movable between a restricting position for contacting leading edges of sheets inserted through an insertion opening to prevent the sheets from being inserted further, and a release position for releasing this restriction. The separation roller is configured to begin rotating after the regulating means has released the restriction on the inserted sheets, and start separating and conveying the sheets one at a time. The feed roller is configured to feed each sheet separated by the separating roller to an image sensor.